I grew up not far from the Golden Gate Bridge in San Francisco, with a 4,200-foot suspension span built in 1937. Regular painting is done to prevent corrosion, and those paint jobs are the main form of maintenance, according to this site:http://goldengatebridge.org/research/facts.php

I just visited the arch bridge over the New River Gorge in West Virginia, where We went across the bridge on the catwalk below the deck. That is a very interesting tour. It is difficult to grasp the magnitude of the structure until you see it that close up. All of that steel loaded in compression is an awsome thing indeed.

The bridges with structual elements in tesion are also amazing, but it is clear that they require a great deal more attention and maintenance to remain safe, since tensile failure modes are usually much faster than compressive failure modes, at least that is my understanding. It would be quite educational to have an explanation of how corrosive failure of the suspension elements is prevented.

I think Mydesign has an excellent point: ancient engineers built amazing, beautiful structures, many of which have lasted hundreds or thousands of years, without any of today's sophisticated design tools. In fact, many prehistorians are still arguing about just how some of the oldest ones got designed and built, meaning what tools the engineers actually had in the way of mathematics and physical tools such as a string and chalk for laying out some of the more sophisticated megalithic monuments.

Notarboca, what type of bridges you like most. The ancient type with brilliant art work of structural engineers or the modern bridges made of steel and concrete mix. The ancient bridges are of excellent master piece works of great engineers. They built it in a very nice way, without the help of structural engineering tools and software for stability analyzes.

While I know investing in infrastructure has become some what of a political hot button, there is investment in that area at least where I live, close to the Altantic and where a major river criss-crosses at numerous points. We've had a number of bridges close for long periods of time (the inconvenience is another story) to be renovated and while it's not as exciting and sexy as the Golden Gate or some of the new bridge projects referenced, it is worthwhile engineering. Even some of these smaller projects are pushing innovation. Check out this story Ann did on a bridge made with recycled plastics.

On vacation in Canada last week I came across the construction site for the new Port Mann bridge in the eastern suburbs of Vancouver. It's a cable-stayed bridge that will replace the old steel arch bridge. The contrast between the two bridges is striking...they are both beautiful and utilize the technology, materials, construction techniques, and aesthetic of their respective eras.

Beth, I think among bridges, construction of hanging bridges are harder and require complex structural designs. The entire structure has to be balanced over the hanging rope and the structural engineers has to possess a good set of design skills for weight balancing.

Henry, most of the ancient bridges, buildings and monuments are look very nicely. We have to really appreciate the designs and the brain behind such projects. Lotus building in Australia, Statue of liberty in US, trade center at burgee Dubai, twin tower at Singapore etc are some of the examples for such brilliant works.

I'm a little spoiled living in San Francisco. I know the Gold Gate Bridge very well. Watching the construction of the new Bay Bridge is exciting. Some of the engineering feats (eg, buildong a new curved ramp leading the the tunnel, cutting out the old part of the bridge and replacing it with the new piece) have been awesome to watch.

One of my favourite bridges is in Washington state over Deception Pass. It's hard to drive across without wanting to stop. Luckily, there are little parking lots on both ends.

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